This invention relates generally to a lift boom assembly for a machine and, more particularly, to a linkage used in the lift boom assembly to maintain a substantially vertical linear path between upward and downward movement of a boom assembly thereof.
It is well known that when conventional lift boom assemblies, mounted at a single pivot axis to a loader frame are raised and lowered, the outer forward ends travel in an arc. When a boom thereof starts to raise, there is forward movement of a supported implement, and, after the pivoting boom goes over center, there is a substantial amount of upward and rearward movement of the implement. This movement tends to shorten the forward reach of the implement when the boom is in a raised position. Therefore, lift boom assemblies for a machine, such as a front-end loader backhoe or skid steer loader, that attempt to control the vertical linear displacement during movement of the boom are well known in the art.
One such example is disclosed in U.S. Pat. No. 5,169,278 issued on Dec. 8, 1992 to Lonnie D. Hoechst, et al. In this patent, a loader boom assembly has articulated lift arms with main and rear lift arm sections pivotally mounted together. The rear lift arm section is pivotally mounted to rear portions of a prime mover frame. The main lift arm section is substantially longer than the rear lift arm section and pivots on the outer end of a rear lift arm link. The lift arm sections are in a folded position when the lift arms are lowered, and a control link is provided to cause the lift arms to unfold as the lift arms are raised to keep the forward portion of the main lift arm section moving along a generally vertical path after a selected lift height. Unfortunately, a first end of the control link is connected adjacent forward portions of the main frame while a second end of the control link extends rearwardly and is pivotally connected to the main lift arm section. In this type of configuration, additional structure must be used at the forward portions of the main frame to support the loads incurred during the movement of the loader boom assembly. Additionally, the length of the control arm is substantially greater than the rear lift link and must be substantial to reach the forward portions of the main frame which increases the likelihood of buckling of the control arms.
Another example is disclosed in U.S. Pat. No. 5,609,464 issued on Mar. 11, 1997 to John M. Moffitt, et al. In this patent, a lift boom assembly includes a pair of laterally spaced, interconnected lift arms having a tool mounted between forward ends thereof. Each lift arm includes a main lift link having upper and lower connecting portions at a rear end thereof. A second lift link is pivotally connected to the upper connecting portion of the main lift link and partially controls movements of the respective lift arm. The opposite end of each second lift link is pivotally connected to a frame of a machine on which the lift assembly is mounted. Movement of the lift arms is further controlled by a pair of control arms. A lower end of each control arm is pivotally connected to the frame. When the boom assembly is in a lowered position relative to the frame, a second or upper end of each control arm extends upwardly and rearwardly from the lower end and is pivotally connected to the lower connecting portion of the respective main lift link. In response to vertical movements of the boom assembly between raised and lowered positions, each control arm swings forwardly and rearwardly of its true vertical position to alter the movements of the lift arms and such that the tool is elevationally moved along a generally linear vertical path. A pair of extendable and retractable drivers provide powered vertical movements to the lift assembly and the tool carried relative to the frame. In this patent, the length of the control arms is again substantially greater than the second lift links which increases the likelihood of control arm buckling. Additionally, the use of the first and second connecting portions of the main lift link for connection with the second lift links and control arms, respectively, requires that the lift arms be manufactured in a manner that increases the weight of the lift arms and the complexity of the design. Therefore, a lift boom assembly that is simple and efficient is needed.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a lift boom assembly is movable between lowered and raised positions and is adapted for use on a work machine. The work machine has a longitudinal centerline, a frame with front and rear end portions including respective front and rear drive axes and upper and lower portions. The lift boom assembly comprises a pair of supports connected to the rear end portion of the frame for supporting the lift boom assembly. A pair of lift arm assemblies are positioned on opposite sides of the longitudinal centerline and are pivotally connected to a respective support. Each of the lift arm assemblies include a main lift link with front and rear end portions and a second lift link. The second lift links each have a first end portion, a second end portion pivotally connected to a respective one of the supports to define a first pivot, and a central portion located between the first and second end portions and pivotally connected to the rear end portion of a respective main lift link to define a second pivot. A pair of extendible and retractable hydraulic actuators are disposed on opposite sides of the longitudinal centerline and connectable between the frame and a respective lift arm assembly for moving the lift boom assembly between the lowered and raised positions. A pair of control links that each have first and second end portions. The first end portion of each of the control links are pivotally connected to a respective one of the supports to define a third pivot. The second end portion of each of the control links are pivotally connected to a respective one of the main lift links to define a fourth pivot. Each of the first, second, third, and fourth pivots are located above the lower portion of the frame.
In another aspect of the present invention, a lift boom assembly is movable between lowered and raised positions and is adapted for use on a work machine. The work machine has a longitudinal centerline, a frame with front and rear end portions including respective front and rear drive axes and upper and lower portions. The lift boom assembly comprises a pair of supports connected to the rear end portion of the frame for supporting the lift boom assembly. A pair of lift arm assemblies are positioned on opposite sides of the longitudinal centerline and are pivotally connected to a respective support. Each of the lift arm assemblies include a main lift link with front and rear end portions and a second lift link. The second lift links each have a first end portion, a second end portion pivotally connected to a respective one of the supports, and a central portion located between the first and second end portions and pivotally connected to the rear end portion of a respective main lift link. A pair of extendible and retractable hydraulic actuators are disposed on opposite sides of the longitudinal centerline and are connected between the frame and a respective lift arm assembly for moving the lift boom assembly between the lowered and raised positions. A pair of control links that each have first and second end portions. The first end portion of each of the control links are pivotally connected to a respective one of the supports. The second end portion of each of the control links are pivotally connected to a respective one of the main lift links. The second end portion of each of the control links extend downwardly and rearwardly from the first end portion of the control links when the lift boom assembly is in the lowered position and upwardly and rearwardly from the first end portion of the control links when the lift boom assembly is in the raised position.
In yet another aspect of the present invention, a work machine has a longitudinal centerline, a frame with front and rear end portions including respective front and rear drive axes and upper and lower portions. The work machine comprises a pair of supports that are connected to the rear end portion of the frame for supporting the lift boom assembly. A pair of lift arm assemblies are positioned on opposite sides of the longitudinal centerline and pivotally connected to a respective support. Each of the lift arm assemblies include a main lift link with front and rear end portions, a mounting brace located beneath and extending from each of the main lift links and located between the front and rear end portions of each of the main lift links, and a second lift link. The second lift links each have a first end portion, a second end portion pivotally connected to a respective one of the supports to define a first pivot, and a central portion located between the first and second end portions and pivotally connected to the rear end portion of a respective main lift link to define a second pivot. A pair of extendible and retractable hydraulic actuators disposed on opposite sides of the longitudinal centerline and connectable between the frame and a respective lift arm assembly for moving the lift boom assembly between the lowered and raised positions. A pair of control links that each have first and second end portions. The first end portion of each of the control links are pivotally connected to a respective one of the supports to define a third pivot. The second end portion of each of the control links being pivotally connected to a respective one of the mounting braces to define a fourth pivot. Each of the first, second, third, and fourth pivots are located above the lower portion of the frame.
The present invention utilizes a lift boom assembly with components having pivots positioned at precise locations on the upper portion of a work machine that cooperate together to achieve a simple and efficient design.